Example with two matches
Input
s = 'cbaebabacd', p = 'abc'
Output
[0, 6]
The substring at index 0 'cba' and at index 6 'bac' are anagrams of 'abc'.
Full lesson preview
Find all anagrams in a string
Find all start indices of p's anagrams in s using a sliding window and frequency counting.
Python practice17 minHashing & SetsIntermediateLast updated March 26, 2026
Problem statement
Given two strings s and p, return a list of all start indices of p's anagrams in s. You may return the answer in any order. An anagram is a permutation of characters. Use a sliding window of length len(p) and maintain counts to detect when the window contains an anagram of p. The output list should be sorted in ascending order (to make testing deterministic).
Task
Use fixed-size sliding window with character counts (hashing) to efficiently detect anagram occurrences in O(n) time.
Examples
Input format
Two strings s and p. Both consist of lowercase letters.
Output format
A list of starting indices (integers) where each index marks the start of an anagram of p in s.
Constraints
0 <= len(s), len(p) <= 10^5. Only lowercase English letters. Aim for O(len(s) + len(p)) time.
Samples
Sample 1
Input
s = 'abab', p = 'ab'
Output
[0, 1, 2]
Windows 'ab','ba','ab' are all anagrams of 'ab'.